This invention concerns a fast acting, re-settable and low cost circuit breaker without moving parts that also has a magnetic amplification feature. The invention can also be used as a current limiter or current sensing. The fast action switching is provided by a Hall device with binary output actuated by a coil. It is operating within microseconds, and it can therefore be used for protecting semiconductors from destruction by overloads. Integrated circuit fabrication processes can be used for manufacturing of this invention. This invention can be used both on a direct current and on alternating current.
This invention has several advantages over previously commercially available circuit breakers. Most existing circuit breakers are of large physical size with many parts, sometimes with a multitude of movable and expensive mechanical parts. These parts wear and create reliability problems. The bulky parts also make it difficult for the designer that is designing existing circuit breakers into an electrical circuit that is to be protected. Other circuit breaker of smaller size, that are available, are not as slow as the circuit breakers mentioned above but they still have a trip time measured in milli-seconds. The present invention has no moving parts, and can be manufactured by integrated circuit processes that means that the total circuit breaker could be in a size of 1 millimeterxc3x971 millimeter with a trip time measured in micro-seconds. In its IC chip form the present invention would also be very inexpensive compared to existing circuit breakers. The present circuit breaker can also operate on both AC and D.C.
Some of the simplest articles for protection of electrical overloads are fuses or so-called wax pellet fuses. These are single use protectors having the disadvantage that they require replacement after the over-current event when the fusing part melts. The incoming household current, today, is normally not protected by fuses but by large size A.C. circuit breakers that trips using a combination of over current and a magnetic relay construction. The majority of these and other large size circuit breakers also have the inconvenience that they have to be manually reset by a push button or by a handle. Both their expensive construction and size limits their use Bi-metallic devices or circuit breakers that operate by heating and bending of the bi-metal have been in use for many years for protecting many different electrical appliances and motors.
When the appliance or motor gets overheated, these thermal devices function as safety devices and thereby prevent fires in the appliance or ignition of other materials around the appliance or electrical machinery. This type of safety device is required by safety organizations such as U.L. and C.S.A.
These so-called thermal cutouts are protecting the devices very well but they are also very slow to actuate. It might take minutes for the device to heat up to the point where they turn off, thereby protecting the device. Some other devices are also on the market. Some of them are called surge absorbers or re-settable fuses that are made from a chemical composition which heats up and increases its resistance when the current gets higher than normal.
The increased resistance limits the current to the electrical circuit, appliance or motor that is normally wired in series with these thermal protectors.
These are also slow acting devices and would not protect semiconductors such as transistors, MOSFETs, S.C.R.s, or TRIACs. Normally the semiconductors mentioned are destructing within perhaps 15 to 30 microseconds.
Faster devices that are on the market have been the so-called solid state sensors, where a coil would actuate a Hall effect device. Most of these have been very large in size and they have also been quite expensive because of its large coil and the complex construction that is common in most of the solid state sensors on the market today.
The circuit breakers or over current type of solid state sensors that are based on a toroid normally have a winding surrounding the uniform cross section of the toroid. If the toroid has a cut in its circumference a Hall device is normally inserted in this cut. The uniform cross section also produces a uniform field, without flux concentration, at the Hall device. The material of the toroid could be of ferrite material, a lamination stack or a solenoid type winding but this does not alter the flux field structure. The larger amount of turns required with this type of structure to actuate the Hall device without tapered flux concentration, makes them by necessity large devices, sometimes in the cubic volume of 1 inch or more. As far as known, in this type of sensor, a tapered electromagnetic flux concentrating structure has not been used. Due to its size and expense they have been limited in their use as circuit breakers; useful only in more expensive appliances such as instruments or used as power line circuit breakers.
These devices and its coils are well understood in the background art and are described basically by: Each turn of one coil wound on such a frame generates xe2x80x9cxxe2x80x9d gauss of flux at one end of the frame or toroid. The coil structure of the background art as well as the coil of the present invention is, of course, governed by Faraday""s law.
The invention concerns a fast acting, re-settable low cost circuit breaker without moving parts that has flux concentrating tapered legs in its ferromagnetic structure, that increases the flux available at its Hall device, thereby providing magnetic amplification. It is also a very small device that can be miniaturized for a circuit board application. It is also a very inexpensive device with only 3 simple components. In addition to being a small inexpensive device, totally without moving parts, it is also a very fast device, operating within microseconds that can protect semi-conductors. It can be operated on both A.C. and D.C. These features (fast operating, re-settable, no moving parts, inexpensive device, small dimensions, and A.C. and D.C. operation) makes this a very useful new invention that can be used in many different forms described below.
Another unique advantage is that this invention can be fabricated by integrated circuit processes by depositing a coil over a deposited ferromagnetic structure. A Hall device can also be deposited in exceptionally close proximity to the ferromagnetic structure thereby efficiently using any available electromagnetic flux generated by its single coil. This makes this invention an unusually sensitive and very efficient circuit breaker or current sensor.
It could be described as a semiconductor chip re-settable circuit breaker comprising:
a current carrying coil producing a variable electromagnetic flux,
a ferromagnetic structure leading said flux towards a Hall device with a binary output, said variable flux causing said output to change.
It could also be described as a monolithic circuit re-settable circuit breaker comprising:
A deposited ferromagnetic material forming a semicircular structure having a central section and two tapered legs, deposited between said legs a Hall device with a binary output, a deposited conducting material forming a coil surrounding said central section wherein when connecting current to said coil an electromagnetic flux is generated in said central section, said flux being concentrated by said legs, in turn causing said Hall output to change state.
The above mentioned integrated circuit fabrication techniques that can be used for this circuit breaker, is somewhat similar to the method used when fabricating integrated circuits, thin film, magnetic write-heads for hard discs. The difference would be, of course, that the magnetic write-head has no Hall device and no binary output and could not be used as a circuit breaker. Integration also gives the possibility of producing extremely close tolerances between the legs and the Hall device for best utilization of available electromagnetic flux. Integration could also be used to produce a micro-type circuit breaker both with close tolerances and low cost.
The present invention can also be manufactured from three separate components that are best described as a circuit breaker without moving parts on a non-magnetic frame having:
a ferromagnetic structure with a central section and two tapered flux concentrating legs, said central section having a larger volume than said two legs, disposed between said legs a Hall device with a binary output, and a coil surrounding said central section, wherein when connecting current to said coil an electromagnetic flux is generated in said central section, said flux being concentrated by said legs, in turn causing said Hall output to change state.
The invention described has a coil surrounding the central section and a tapered flux concentrating feature in its legs.
Textbooks are giving the basic theory about the magnetic flux available when the frame structure is tapered or has a diminishing area away from the coil. This concentrates the electromagnetic flux lines generated under the central section and then leading them into a smaller ferromagnetic area. This concentrates the flux and can be called magnetic amplification. Theory also states that flux lines cannot be destroyed, and that flux lines follow a ferromagnetic material rather than air, therefore the concentrated flux lines appear at the gap or legs at a higher Gauss level.
During experimentation and reduction to practice of the different forms of circuit breakers of the present invention, somewhat unexpected high electromagnetic flux levels with low coil current have been achieved.
Textbooks are stating that the electromagnetic flux field in the gap, [with a steady inducing current]:
Equals the volume (area) of structure under the coil divided by the volume (area) of the gap. Therefore if the volume of the central section under the coil in the present invention is twice as large as the volume of the two legs, then the flux level at the gap is theoretically twice as large, as if both the central section and the legs were of the same volume. Even though this formula is available in textbooks it is believed that this fact has not been applied to the construction of circuit breakers or solid state sensors in the background art.
Another advantage with the present invention is that it can go into a latched state; in other words, it would shut down the current to the electrical device, motor or machinery that it is used on, until the fault condition has been corrected. This latching function is available in commercially available Hall devices and are reset by turning off the power or reversing the current in the coil.
The invention could also be used as a continuous current monitor.
For example, used as a Wattmeter that requires both a current and a voltage input; both are provided by the present invention.
There is always an advantage with a higher output out of any device; it follows that less further electronic amplification is required.
Therefore the magnetic amplification that takes place in this invention and the larger amount of electromagnetic flux available, makes this a circuit breaker easily interfaced with other semiconductors.
If the invention is fabricated using a commercially available Hall device placed in close proximity to its legs it could drive either what is called a Hall I.C. or Hall sensor.
These are available from many manufacturers in different closeness of tolerance and pricing. They are available either as a Hall switch, Hall latch or as a linear Hall sensor. Due to the flux concentrating at the legs in this invention it requires only a few turns of its coil, on its central section, to get the necessary electromagnetic flux to change the state of the Hall device thereby providing circuit breaker action.
Commercial Hall devices are available with current capabilities of up to 1000 milli amperes which would also be the maximum current capability of the circuit breaker. By the addition of a power semiconductor such as an MOSFET, TRIAC, or S.C.R driven by this inventions binary output, the final current capability can easily be extended to hundreds of amperes.
The Hall device cannot be damaged by being driven by large flux levels since it does not have an upper magnetic limit.
The circuit breaker of this invention can be used to protect a motor such as a brushless motor that normally is driven by a multitude of MOSFETs. The coil of the invention would normally be connected in series with the power supply to the motor. Normal current to the motor, determined by the number of turns in the coil and the sensitivity of the Hall device, would allow the motor to run normally. If a fault condition should occur, the current through the coil would increase, tripping the Hall device to its closed position thereby pulling all of the gates of the MOSFETs to ground, instantaneously providing a circuit breaker function; removing all current to the motor. This type of application is depicted in FIG. 6.